well youre either driving like a complete a**hole or your speedo is off.

haha far from it. I drive my ranger extremely conservatively, I always try to keep it at or under 2500 rpm which is near impossible on the hwy. once I get to 70 its around 3000+ rpm. Whenever I fill up its around 13 gallons which seemed pretty small to me seeing as how my tacoma was around 18 gallons. So it seems like my speedometer must be off, which I was already under the suspicion that it might be, but when I drove past one of devices that tell you how fast your going it was only off by a couple mph. How would I go about calibrating it?